The Arabidopsis sugar‐insensitive mutants sis4 and sis5 are defective in abscisic acid synthesis and response

Abstract

SummaryAlthough soluble sugar levels affect many aspects of plant development and physiology, little is known about the mechanisms by which plants respond to sugar. Here we report the isolation of 13 sugarinsensitive (sis) mutants of Arabidopsis that, unlike wild-type plants, are able to form expanded cotyledons and true leaves when germinated on media containing high concentrations of glucose or sucrose. The sis4 and sis5 mutants are allelic to the ABA-biosynthesis mutant aba2 and the ABAinsensitive mutant abi4, respectively. In addition to being insensitive to glucose and sucrose, the sis4/ aba2 and sis5/abi4 mutants also display decreased sensitivity to the inhibitory effects of mannose on early seedling development. Mutations in the ABI5 gene, but not mutations in the ABI1, ABI2 or ABI3 genes, also lead to weak glucose-and mannose-insensitive phenotypes. Wild-type and mutant plants show similar responses to the effects of exogenous sugar on chlorophyll and anthocyanin accumulation, indicating that the mutants are not defective in all sugar responses. These results indicate that defects in ABA metabolism and some, but not all, defects in ABA response can also alter response to exogenous sugar.

Impaired sucrose‐induction mutants reveal the modulation of sugar‐induced starch biosynthetic gene expression by abscisic acid signalling

“…The isi4/gin1 mutants were found to display ABA-de®cient phenotypes, and their proposed identity as alleles of aba2 is discussed. Our results show that sugar induction of starch biosynthetic genes, like carbohydrate repression of seedling development and concomitant induction of photosynthetic gene expression (ArenasHuertero et al, 2000;Huijser et al, 2000;Laby et al, 2000), depends on ABA signalling. Arenas-Huertero et al (2000) recently suggested that glucose responses were mediated through ABA signalling.…”

“…Mutants in abi4 have now been isolated in a number of genetic screens, all involving selection at the seedling stage. Originally isolated as a mutant germinating in the presence of ABA (Finkelstein et al, 1998), it also shows germination and seedling establishment on high glucose, sucrose and mannose (Arenas-Huertero et al, 2000;Huijser et al, 2000;Laby et al, 2000;this study), and high salinity and osmolarity (Quesada et al, 2000). This suggests that in abi4 mutants, a variety of external stimuli no longer inhibit a program of seedling establishment.…”

“…Two of the isi mutants isolated (isi3 and isi4) were found to be allelic to mutants identi®ed in sugar-sensing screens based on seedling development (Arenas-Huertero et al, 2000;Huijser et al, 2000;Laby et al, 2000). These groups reported that the sun6, sis5 and gin6 mutants were alleles of abscisic acid insensitive4, and that known aba and abi mutants exhibited glucose insensitive phenotypes.…”

Arabidopsis extra‐large G proteins (XLGs) regulate root morphogenesis

“…XLGs modulate sensitivity to sugar, ABA and ethylene Increased root length in the presence of sucrose is a characteristic of some sugar-insensitive mutants (Laby et al, 2000), and conventional heterotrimeric G proteins are involved in sugar sensing Huang et al, 2006). As the experiments reported in Figure 4(b-d) were performed in the presence of 1% sucrose, which is a standard media composition, we further evaluated the effects of sucrose concentrations ranging from 0.5% to 10% on the root length phenotype of the xlg triple mutant (Figure 6a,b).…”

EXORDIUM-LIKE1 Promotes Growth during Low Carbon Availability in Arabidopsis

“…For example, abscisic acid-deficient or abscisic acidinsensitive mutants are Glc insensitive (ArenasHuertero et al, 2000;Huijser et al, 2000;Laby et al, 2000;Cheng et al, 2002). Ethylene overproduction mutants and mutants with constitutive ethylene signaling show reduced responses to high levels of Glc or Suc, whereas ethylene-insensitive mutants are hypersensitive to sugar (Zhou et al, 1998;Cheng et al, 2002).…”